Radioactive barium sulphate is found in many subterraneum oil and gas deposits in small quantities. Over a period of years, radioactive barium sulphate gradually becomes coated onto the inside surfaces of tubulars (pipes), flanges, valves and related fluid carrying equipment used in extracting oil and gas from subterraneum deposits. The radioactive barium sulphate forms a scale on the inside of the fluid carrying equipment that in a 41/2" OD, 4" ID pipe may be an inch thick or more, almost completely blocking the pipe. Such a pipe becomes useless for the transportation of fluid, and must be disposed of.
Before such a pipe or other fluid carrying equipment contaminated with radioactive barium sulphate scale may be disposed of, for example in underground storage, the regulations of some jurisdictions require that the radioactive scale be removed. Radioactive barium sulphate contains radium 226 which is a dirty isotope with a half life of 1600 years. If ingested, inhaled or absorbed into human tissue, it ends to migrate directly to the lymph glands or bone marrow and cause cancer. A safe procedure for the removal of scale is far more important than recovery or utilizing the equipment after cleaning. This is a unique and difficult problem in that the dimensions of the fluid carrying equipment vary in size greatly and operative equipment such as valves are difficult to access in order to clean them
One way of removing the scale is to use a rotary scraping tool that bores out the pipe, but this method tends to cause hazardous radioactive dust to form, even when the equipment and environment is wetted. Because of the hazard caused by the formation of radioactive dust, workers must use specialized protective clothing and use remote air supplies when working to remove radioactive scale using a boring process. Also, the method is inapplicable to valves, and useful only for tubulars having constant diameter. Another way to remove the radioactive scale is to apply ethylenediaminetetraacetic acid to the scale, but this too has limited success. Other ways include percussion hammering and use of extreme high pressure water, but neither are particularly useful for valves and both methods are time consuming, expensive and require hazardous equipment. Both dry and high pressure water cleaning tend to carry minute radioactive dust particles that are potentially very hazardous to the worker's health.
The inventor has provided a completely new method of removing radioactive scale from fluid carrying equipment that includes, according to one aspect of the invention, initially cryogenically treating the equipment, followed by applying an aqueous solution to the scale and subsequently impacting the equipment to remove the scale. The preferred aqueous fluid is water, and it is believed to be advantageous to apply hot water to the scale.